obj1=Graphics[{Red,Rectangle[{0,0},{1,1}]}]

Show[obj1,AspectRatio->1]

line0[x_,x0_,y0_]:=y0
line1[x_,x0_,y0_]:=-1(x-x0)+y0
line2[x_,x0_,y0_]:=1(x-x0)+y0

Plot[{2,line1[x,1,2]},{x,1,2}]

one=Plot[{line0[x,1,2],line1[x,1,2]},{x,1,2},AspectRatio->1,PlotRange->{{0,2},{0,2}},Filling->{1}]

two=Plot[{line1[x,1,2],line2[x,2,1]},{x,1.5,2},AspectRatio->1,PlotRange->{{0,2},{0,2}},Filling->{1}]

three=Plot[{line2[x,1.5,1],line0[x,1,0.5]},{x,4/4,1.5},AspectRatio->1,PlotRange->{{0,2},{0,2}},Filling->{1}]

four=Plot[{line0[x,1.5,1],line0[x,1,0.5]},{x,4/4,1.5},AspectRatio->1,PlotRange->{{0,2},{0,2}},Filling->{1}]

Show[one,two,three]